This invention relates to a curable polymer composition. More particularly, this invention relates to a solvent soluble polyene-polythiol curable composition, method of preparing the same, as well as curing the polyene-polythiol composition in the presence of a free radical generator to solid, cross-linked solvent-insoluble materials.
It is known that polyenes are curable by polythiols in the presence of free radical generators such as actinic radiation to solid polythioether containing resinous or elastomeric products. The commercially available polythiols, e.g., mercaptocarboxylate esters of polyols used in curing afford cured polythioether products having a low percent elongation on failure. However there are several end uses wherein a coating must have a relatively high elongation in order to be operable. For example it is necessary that a coating on a bottle cap have a relatively high elongation since after it is applied and cured on the metal blank, the blank is subsequently formed by extrusion or otherwise into cap form which necessitates that the coating have sufficient elongation to follow the contours of the thus formed cap without rupture. Additionally in bottle coating it is necessary that the cured coating have high elongation to prevent glass shattering. Thus a curable coating having a high elongation after curing is desirous.
In accordance with this invention, a curable polymer composition can be prepared from compatible polyene and polythiol components derived from a hydantoin glycol. This polyene and polythiol mixture is a highly reactive composition which is capable of being photocured when exposed to actinic radiation in the presence of a UV sensitizer to insoluble polythioether containing materials which exhibit excellent physical and chemical properties. For example, wire coatings formed from the cured polyene and polythiol composition are capable of withstanding severe temperature environments for extended periods. The subject cured materials resist strongly acid etching solutions or high alkaline conditions. Additionally the cured polythioether product from the polyenes and polythiols herein has remarkable flexibility and high elongation at failure as will be shown in an example hereinafter. The desirable characteristics of the cured materials make the hydantoin glycol derived poly-polythiol curable composition particularly useful as coatings on wire and formable metals.
Generally speaking, the novel curable composition is comprised of a polyene component containing at least 2 reactive carbon to carbon unsaturated bonds per molecule which is a reaction product of N,N'-bis(2-hydroxyethyl) dimethylhydantoin and at least one unsaturated organic compound such as ene-acid or ene-isocyanate; and a polythiol component containing at least two thiol groups, which is the reaction product of N,N'-bis(2-hydroxyethyl) dimethylhydantoin and a mercaptocarboxylic acid.
The formation of such polyenes may be schematically represented by the following nonlimiting equation, wherein the unsaturated organic compound reactant is an ene-isocyanate having reactive allylic end groups as illustrated by a reaction product of one mole of 2,4-toluene diisocyanate with one mole of allyl alcohol: ##STR1##
Similarly, the formation of the polythiol may be represented by the nonlimiting equation illustrating .beta.-mercaptopropionic acid as the mercaptocarboxylic reactant: ##STR2##
Furthermore, the hydantoin glycols are generally commercially availabe materials. The operable hydantoin glycols include not only N,N'-bis(2-hydroxyethyl) dimethylhydantoin, but also polyethoxylated derivatives thereof. These polyethoxylated derivatives are formed by the addition of the desired number of moles of ethylene oxide to the N,N'-bis(2-hydroxyethyl) dimethylhydantoin, i.e., by a conventional epoxide ring-opening addition reaction.
The aforedescribed hydantoin glycols are operable starting materials for the formation of both the polyene and polythiol.
In the curable polyene-polythiol containing compositions, the hydantoin glycols backbone may be either identical or different for both the polyene and polythiol components.
One group of operable polyenes containing hydantoin glycol backbones are unsaturated urethane derivatives. These polyenes, i.e., unsaturated urethane derivatives of hydantoin glycol may be represented by the general formula: ##STR3## wherein Q is the hydantoin glycol moiety remaining after the two hydroxyl groups of the hydantoin glycol have reacted to form two urethane, i.e., ##STR4## linkages; A and B are polyvalent organic radical members free of reactive carbon to carbon unsaturation and containing group members such as aryl, substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substituted cylcoalkyl, alkyl and substituted alkyl containing 1 to 36 carbon atoms and mixtures thereof. These group members can be connected by a chemically compatible linkage such as --O--, --S--, carboxylate, carbonate, carbonyl, urethane and substituted urethane, urea and substituted urea, amide and substituted amide, amine and substituted amine and hydrocarbon. Z is a divalent chemically compatible linkage such as ##STR5## --O-- and --S--, preferably ##STR6##
Preferred examples of operable aryl members are either phenyl or naphthyl, and of operable cycloalkyl members which have from 3 to 8 carbon atoms. Likewise, preferred substituents on the substituted members may be such groups as chloro, bromo, nitro, acetoxy, acetamido, phenyl, benzyl, alkyl and alkoxy of 1 to 9 carbon atoms, and cycloalkyl of 3 to 8 carbon atoms.
X is a member selected from the group consisting of:
a. --(CH.sub.2).sub.d --CR'=CHR
b. --O(CH.sub.2).sub.d --CR'=CHR
c. --S--(CH.sub.2).sub.d --CR'=CHR
d. --(CH.sub.2).sub.d --C.tbd.CR
e. --O--(CH.sub.2).sub.d --C.tbd.CR
f. --S--(CH.sub.2).sub.d --C.tbd.CR
and mixtures thereof; and R and R' each are independently either a hydrogen or methyl radical, preferably a hydrogen radical; and d, p and q each are integers from 0 to 1; y is an integer from 1 to 10, preferably 1 to 5; r is an integer of at least 1, preferably from 1 to 4, and more particularly from 1 to 2.
As used herein, polyenes and polyynes refer to simple or complex species of alkenes or alkynes having a multiplicity of pendant or terminally reactive carbon to carbon unsaturated functional groups per average molecule. For example, a diene is a polyene that has two reactive carbon to carbon double bonds per average molecule, while a diyne is a polyyne that contains two reactive carbon to carbon triple bonds per average molecule; a solid polyene which is a reaction product of a styene-allyl alcohol copolymer having about 8 hydroxyl groups per average molecule and a reactive unsaturated monoisocyanate having one terminal reactive carbon to carbon double bond per average molecule is a complex polyene which contains in its structure 8 reactive carbon to carbon double bonds per average molecule. For purposes of brevity, all these classes of compounds will be referred to hereafter as polyenes.
In defining the position of the reactive functional carbon to carbon unsaturation, the term terminal is intended to mean that functional unsaturation is at an end of the main chain in the molecule. The term pendant means that the reactive carbon to carbon unsaturation is located terminal in a branch of the main chain as contrasted to a position at or near the ends of the main chain. For purposes of brevity, all of these positions are referred to herein generally as terminal unsaturation.
Functionality as used herein refers to the average number of ene or thiol groups per molecule in the polyene or polythiol, respectively. For example, a triene is a polyene with an average of three reactive carbon to carbon unsaturated groups per molecule, and thus has a functionality (f) of three. A dithiol is a polythiol with an average of two thiol groups per molecule and thus has a functionality (f) of two.
The term reactive unsaturated carbon to carbon groups means groups which will react under proper conditions as set forth herein with thiol groups to yield the thioether linkage ##STR7## as contrasted to the term unreactive carbon to carbon unsaturation which means ##STR8## groups found in aromatic nuclei (cyclic structures exemplified by benzene, pyridine, anthracene, and the like) which do not under the same conditions react with thiols to give thioether linkages. For purposes of brevity, this term will hereinafter be referred to generally as reactive unsaturation or a reaction unsaturated compound.
As used herein, the term polyvalent means having a valence of two or greater.
A general method of forming the urethane-containing hydantoin glycol based polyene is to react the hydantoin glycol material represented by a general formula Q-(OH).sub.2, in which Q is as hereinbefore set forth; with at least one reactive unsaturated isocyanate of the general formula ##STR9## in which the members A, Z, B, X and the integers p, q, y and r are as hereinbefore set forth.
The term reactive unsaturated isocyanate will hereinafter be referred to as an ene-isocyanate or an yne-isocyanate.
The reaction is carried out in a moisture free atmosphere at atmospheric pressure at a temperature in the range from about 30.degree. to 100.degree. C, preferably from about 40 to 80.degree. C, for a period of about 10 minutes to about 24 hours. The reaction is preferably a one step reaction wherein all the reactants are charged together. The ene-isocyanate or yne-isocyanate is added in a stoichiometric amount necessary to react with the hydroxy groups in the hydantoin glycol. The reaction, if desired, may be carried out in the presence of a catalyst and inert solvent. Operable non-limiting catalysts include tin catalysts such as dibutyl tin dilaurate, stannous octoate; tertiary amines such as triethylene diamine or N,N,N',N'-tetramethyl-1,3-butanediamine, etc. Useful inert solvents include aromatic hydrocarbons, halogenated saturated aliphatic or aromatic hydrocarbons and mixtures thereof. Representative non-limiting examples include benzene, chlorobenzene, chloroform, 1,1,1-trichloroethane, 1,2-dichloroethane and the like.
Operable ene- or yne- isocyanates having the above defined general formula include, but are not limited to, simple monoeneisocyanates such as allyl isocyanate, 2-methallyl isocyanate, crotyl isocyanate, etc.
The aforementioned reactive unsaturated isocyanates are a group of compounds having the above general formula of operable ene- or yne-isocyanates wherein the integers p and q are 0 and r is 1. Thus, the urethane hydantoin glycol based polyenes formed from these reactive unsaturated isocyanates may be represented by simplifying the general formula for the polyenes to the following specific formula: ##STR10## wherein preferably y is 1 and the other members being as hereinbefore set forth.
Other operable ene- or yne-isocyanates are those prepared by reacting a polyisocyanate of the general formula ##STR11## in which x is at least 2 and A is as hereinbefore set forth; with a reactive unsaturated alcohol of the general formula ##STR12## in which B, X and y are as hereinbefore set forth.
The above polyisocyanate and alcohol reactants are added in such stoichiometric amounts that x-1 isocyanate groups react to give x-1 urethane linkages.
Operable non-limiting examples of starting polyisocyanate reactants include hexamethylenediisocyanate, tolylene diisocyanate, xylylene diisocyanate, methylenebis(phenyl isocyanate), 4,4'-methylene(cyclohexyl isocyanate), 1-methoxy-2,4,6-benzenetrisocyanate, 2,4,4'-triisocyanatodiphenylether, diphenylmethane tetraisocyanates, polyisocyanates having various functional groups such as N,N',N"-tris(isocyanatohexyl)-biuret or adducts of polyalcohols and diisocyanates which have at least 2 free isocyanate groups. Adduct of trimethylolpropane and 3 moles of toluene diisocyanate, is suitable.
Illustrative of the operable reactive unsaturated alcohols which may react with the polyisocyanates to give the desired eneisocyanate include but are not limited to allyl and methallyl alcohol, crotyl alcohol, crotyl alcohol,.omega. -undecylenyl alcohol, 2-vinyloxyethanol, vinylhydroxyethyl sulfide, propargyl alcohol, 1-allylcyclopentanol, 2-methyl-3-butene-2-ol. Reactive unsaturated derivatives of polyhydric alcohols such as glycols, triols, tetraols, etc., are also suitable. Representative examples include trimethylolpropane or trimethylolethane diallyl ethers, pentaerythritol triallyl ether and the like. Mixtures of various reactive unsaturated alcohols are operable as well. A suitable ene-isocyanate prepared by treating one mole of trimethylbenzene triisocyanate with two moles of trimethylolpropane diallyl ether. The resulting urethane containing ene-isocyanate is a polyene havin four reactive allyl ether groups per molecule. Mixtures of various ene- or yne-isocyanates are operable as well.
Another class of polyenes operable in forming the curable polyene-polythiol system of the subject invention are esters of hydantoin glycol. Similarly, these polyenes may be represented by the general formula: ##STR13## wherein Q is the hydantoin glycol moiety remaining after removal of the 2 hydroxyl groups from the said hydantoin glycol thereby forming an ester linkage; the members A, B, and X and integers p, q, y and r are as hereinbefore set forth in the urethane containing hydantoin glycol based polyene and k is an integer from 0 to 1.
A general method of forming these esters is to react the hydantoin glycol represented by the aforedefined general formula ##STR14## with at least one reactive unsaturated monocarboxylic acid of the general formula: ##STR15## in which the members A, B and X, and the integers, k, p, q, y and r are as hereinbefore set forth. The term reactive unsaturated carboxylic acid will hereinafter be referred to as an ene- and/or an yne-acid.
The esterification reaction may be carried out in a conventional manner in the presence of an acid catalyst, the water formed during the reaction being removed as an azeotrope.
Operable ene- or yen-acids include but are not limited to simple monoene-acids such as acrylic acid, methacrylic acid, vinylacetic acid, 5-hexenoic acid, 6-heptynoic acid, propiolic acid and the like.
These aforementioned reactive unsaturated acids are a group of acids having the above general formula of operable ene- or yne-acids wherein the integers p and q are 0, and r is 1. Thus the ester containing hydantoin glycol based polyenes formed from these reactive unsaturated acids may be represented by simplifying the general formula for the polyenes to the following specific formula: ##STR16## which, preferably, y is 1 and the other members being as hereinbefore set forth.
Other operable acids are those containing more than one terminally reactive unsaturated group in the molecule. These may be prepared by reacting a polycarboxylic acid of the general formula A--(COOH).sub.x, in which x is at least 2 and A is as hereinbefore set forth, with reactive unsaturated alcohol of the general formula [(X).sub.y --B]--OH, in which B, X and y are as hereinbefore set forth.
The above polycarboxylic acid and alcohol reactants are added in such stoichiometric amounts that x-1 carboxylic groups react to give x-1 ester linkages.
Operable polycarboxylic acids include but are not limited to dicarboxylic acids such as adipic, tartaric, succinic, terephthalic, etc.
Operable reactive unsaturated alcohol components are the same as described above as being suitable in forming ene-isocyanates. As an example, a suitable ene-acid can be prepared by reacting one mole of trimethylolpropane diallyl ether with one mole of succinic anhydride in the presence of pyridine as a solvent. The resulting succinate product contains a free carboxylic group as well as two reactive allyl ether groups.
The polythiol component of the curable composition is mercaptoester having two thiol groups per molecule. The polythiol is a reaction product of hydantoin glycol and at least one mercaptocarboxylic acid. The polythiol may be represented by the following general formula: ##STR17## and E is the hydantoin glycol moiety remaining after removal of the 2 hydroxyl groups from the hydantoin glycol thereby forming 2 ester linkages; R.sub.3 is a polyvalent organic radical member free of reactive carbon to carbon unsaturation and contains group members such as aryl, substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl and substituted alkyl groups containing 1 to 16 carbon atoms.
Preferred examples of operable aryl members are either phenyl or naphthyl, and of operable cycloalkyl members which have from 3 to 8 carbon atoms. Likewise, preferred substituents on the substituted members may be such groups as chloro, bromo, nitro, acetoxy, acetamido, phenyl, benzyl, alkyl and alkoxy of 1 to 9 carbon atoms, and cycloalkyl of 3 to 8 carbon atoms.
Operable hydantoin glycols are those of the formula: ##STR18##
wherein m + n are 2 to 22 and m and n are each at least 1.
Operable mercaptocarboxylic acids include but are not limited to thioglycollic acid (mercaptoacetic acid), .alpha.-mercaptopropionic acid, .beta.-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptovaleric acids, mercaptoundecyclic acid, mercaptostearic acid, and o- and p-mercaptobenzoic acids. Preferably, thioglycollic or .beta.-mercaptopropionic acid is employed. Mixtures of various mercaptocarboxylic acids are operable as well.
The polythiol esters are prepared by the esterification of the hydantoin glycol with mercaptocarboxylic acid in the presence of an acid catalyst, the water formed during the reaction being removed as an azeotrope in a suitable solvent.
The reaction is carried out at atmospheric pressure at a temperature in the range of from 60 to about 150.degree. C, preferably from 60.degree. to 110.degree. C. for a period of 30 minutes to about 24 hours.
Suitable acid catalysts include but are not limited to p-toluenesulfonic acid, sulfuric acid, hydrochloric acid and the like. Useful inert solvents include but are not limited to saturated aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, ethers, ketones, etc. Representative nonlimiting examples of solvents include toluene, benzene, xylene, chloroform, 1,2-dichloroethane, etc.
In summary, by admixing the novel hydantoin glycol based polyenes and polythiols and thereafter exposing the mixture at ambient conditions to a free radical generator, a solid, cured insoluble polythioether product having a high percent elongation is obtained.
Prior to curing, the polyene and polythiol components are admixed in a suitable manner so as to form a homogeneous solid curable mixture. Thus, the polyene and polythiol reactants can be admixed without the necessity of using a solvent at room temperature or slightly elevated temperatures up to about 80.degree. C when one of the components is a solid or, if desired, the reactants may be dissolved in a suitable solvent and thereafter the solvent can be removed by suitable means such as evaporation.
To obtain the maximum strength, solvent resistance, creep resistance, heat resistance and freedom from tackiness, the reactive components consisting of the polyenes and polythiols are formulated in such a manner as to give solid, crosslinked, three dimensional network polythioether polymer systems on curing. In order to achieve such infinite network formation, the individual polyenes and polythiols must each have a functionality of at least 2 and the sum of the functionalities of the polyene and polythiol components must always by greater than 4. Blends and mixtures of various polyenes and various polythiols containing said functionality are also operable herein.
The compositions to be cured in accord with the present invention may, if desired, include such additives as antioxidants, accelerators, dyes, inhibitors, activators, fillers, thickeners, pigments, anti-static agents, flame-retardant agents, surface-active agents, extending oils, plasticizers and the like within the scope of this invention. Such additives are usually pre-blended with the polyene or polythiol prior to or during the compounding step. The aforesaid additives may be present in quantities up to 500 or more parts based on 100 parts by weight of the polyene-polythiol curable compositions and preferably 0.005-300 parts on the same basis.
The polythioether-forming components and compositions, prior to curing may be admixed with or blended with other monomeric and polymeric materials such as thermoplastic resins, elastomers or thermosetting resin monomeric or polymeric compositions. The resulting blend may be subjected to conditions for curing or co-curing of the various components of the blend to give cured products having unusual physical properties.
Although the mechanism of the curing reaction is not completely understood, it appears most likely that the curing reaction may be initiated by most any free radical generating source which dissociates or abstracts a hydrogen atom from an SH group, or accomplishes the equivalent thereof. Generally, the rate of the curing reaction may be increased by increasing the temperature of the composition at the time of initiation of cure. In most applications, however, the curing is accomplished conveniently and economically by operating at ordinary room temperature conditions.
Operable curing initiators or accelerators include radiation such as actinic radiation, e.g., ultraviolet light, lasers; ionizing radiation such as gamma radiation, x-rays, corona discharge, etc.; as well as chemical free radical generating compounds such as azo, peroxidic, etc., compounds.
Azo or peroxidic compounds (with or without amine accelerators) which decompose at ambient conditions are operable as free radical generating agents capable of accelerating the curing reaction include benzoyl peroxide, di-t-butyl peroxide, cyclohexanone peroxide with dimethyl aniline or cobalt naphthenate as an accelerator; hydroperoxides such as hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxides; peracid compounds such as t-butylperbenzoate, peracetic acid; persulfates, e.g., ammonium persulfate; azo compounds such as azobis-isobutyronitrile and the like.
The free radical generating agents are usually added in amounts ranging from about 0.001 to 10 percent by weight of the curable solid polyene-polythiol composition, preferably .01 to 5 percent.
The curing period may be retarded or accelerated from less than 1 minute to 30 days or more.
Conventional curing inhibitors or retarders which may be used in order to stabilize the components or curable compositions so as to prevent premature onset of curing may include hydroquinone; p-tert-butyl catechol; 2,6-di tert-butyl-p-methylphenol; phenothiazine; N-phenyl-2-naphthylamine; phosphorous acid; pyrogallol and the like.
The preferred free radical generator for the curing reaction is actinic radiation, suitably in the wavelength of about 2,000 to 7,500A, preferably for 2,000 to 4,000A.
A class of actinic light useful herein is ultraviolet light and other forms of actinic radiation which are normally found in radiation emitted from the sun or from artificial sources such as Type RS Sunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps, tungsten halide lamps and the like. Ultraviolet radiation may be used most efficiently if the photocurable polyene/polythiol composition contains a suitable photocuring rate accelerator. Curing periods may be adjusted to be very short and hence commercially economical by proper choice of ultraviolet source, photocuring rate accelerator and concentration thereof, temperature and molecular weight, and reactive group functionality of the polyene and polythiol. Curing periods of less than about 1 second duration are possible, especially in thin film applications such as desired for example, in coatings, adhesives and photoimaged surfaces.
Various photosensitizers, i.e., photocuring rate acclerators are operable and well known to those skilled in the art. Examples of photosensitizers include, but are not limited to, benzophenone O-methoxybenzophenone, acetophenone, O-methoxyacetophenone, acenaphthene-quinone, methyl ethyl ketone, valerophenone, hexanophenone, .alpha. -phenylbutyrophenone, p-morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone, benzoin, benzoin methyl ether, 4'-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone, benzaldehyde, O-methoxybenzaldehyde, .alpha.-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene, thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]anthracen-7-one, 1-naphthaldehyde, 4,4'-bis (dimethylamino)benzophenone, fluorene-9-one, 1'-acetonaphthone, 2'-acetonaphthone, triphenylphosphine, tri-o-tolylphosphine, acetonaphthone and 2,3-butanedione, benz[a]anthracene 7,12 dione, etc., which serve to give greatly reduced exposure times and thereby when used in conjunction with various forms of energetic radiation yield very rapid, commercially practical time cycles by the practice of the instant invention.
These photocuring rate accelerators may range from about 0.005 to 50 percent by weight of the photocurable polyenepolythiol composition, preferably 0.05 to 25 percent.
The mole ratio of the ene/thiol groups for preparing the curable composition is from about 0.2/1.0 to about 8/1.0, and preferably from 0.5/1.0 to about 2/1.0 group ratio.
The curable hydantoin glycol derived polyene and polythiol compositions are used in preparing solid, cured crosslinked insoluble polythioether polymeric products having many and varied uses, examples of which include, but are not limited to, coatings; adhesives; films; molded articles; imaged surfaces, e.g., solid photoresists; solid printing plates; e.g., offset, lithographic, letterpress, gravures, etc., silverless photographic materials and the like.
Since the cured materials formed from the polyenepolythiol composition posses various desirable properties such as resistance to severe chemical and physical environments and have a high percent elongation, they are particularly useful for preparing coatings.
A general method for preparing coatings, comprises coating the curable composition on a solid surface of a substrate such as plastic, rubber, glass, ceramic, metal, paper and the like; exposing directly to radiation, e.g., U.V. light until the curable composition cures and crosslinks in the exposed areas. The resulting products are cured coatings on suitable substrates or supports.
In forming the composition comprised of the polythiol and the polyene, it is desirable that the photocurable composition contain a photocuring rate accelerator from about 0.005 to 50 parts by weight based on 100 parts by weight of the aforementioned polyene and polythiol.
It is to be understood, however, that when energy sources, e.g., ionizing radiation, other than visible or ultraviolet light, are used to initiate the curing reaction, photocuring rate accelerators (i.e., photosensitizers, etc.) generally are not required in the formulation.
When U.V. radiation is used for the curing reaction, a dose of 0.0004 to 6.0 watts/cm.sup.2 is usually employed.
The following examples will aid in explaining, but should not be deemed limiting, the instant invention. In all cases unless otherwise noted, all parts and percentages are by weight.